(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD) device having an improved backlight unit and, more particularly, to the improvement of the structure of the optical sheet assembly in the backlight unit of the LCD device.
(b) Description of the Related Art
An LCD device has the advantages of smaller thickness and lightweight, and thus is used as a flat display panel in a variety of applications. The LCD device generally includes a display panel, a backlight unit for irradiating the display panel from the rear surface thereof, a housing for receiving therein the display panel and the backlight unit in one body so that the front screen of the display panel is exposed from a front opening of the housing, and a backlight chassis for positioning the backlight unit with respect to the LCD panel within the housing.
FIG. 1 shows a typical LCD device 10 in an exploded view thereof. The LCD device 10 includes an LCD panel 12 having a front screen, a backlight unit 14 disposed at the rear side of the LCD panel 12 for irradiating the LCD panel at the rear side, and a housing including a frame member 16 and a pair of holders 18 which support the LCD panel 12 and the backlight unit 14 at the top and bottom sides of the LCD panel in association with the frame member 16, and a backlight chassis (not shown) for positioning the backlight unit 14 with respect to the LCD panel 12 within the housing. The LCD panel 12 mounts thereon drive circuits 32 and 34 at the edge of the LCD panel 12.
The frame member 16 is made of a metallic body 16 which defines a window 20 for exposing therethrough the front screen of the LCD panel 12. The frame member 16 acts as an electrostatic shield for the LCD device. The frame member 16 is engaged with the holders 18 to thrust the LCD panel 12 toward the backlight unit 14.
FIG. 2 shows the top corner of the typical LCD device 10, in a sectional view taken along line IIxe2x80x94II in FIG. 1.
In FIG. 2, the LCD panel 12 includes a color filter 26 and a TFT substrate 28, which are sandwiched between a first (front) polarizing plate 22 and a second (rear) polarizing plate 24. A black matrix 30 is disposed between the color filter 26 and the TFT substrate 28 to cover the periphery of the TFT substrate 28 for preventing the backlight from passing the LCD panel 12.
The backlight unit 14 includes a light source 36 for emitting light, an optical guide plate 38 made of acrylic resin for passing therethrough the light emitted by the light source 36, and a laminated, optical sheet assembly 48 including a first light scattering sheet 40, a first lens sheet 42, a second lens sheet 44 and a second light scattering sheet 46, which are consecutively formed on the front surface of the optical guide plate 38. A reflective sheet 50 is formed on the rear surface of the optical guide plate 38 for reflecting the light passing the rear surface of the optical guide plate 38 toward the internal thereof.
The optical guide plate 38 receives light from the light source 36 at the light receiving edge 38b thereof and passes the received light through the front surface 38a thereof. The first and second light scattering sheets 40 and 46 have a function for scattering the light passing therethrough to obtain a uniform brightness of the front screen. The first and second lens sheets 42 and 44 are made of a plastic material having a thickness of about 0.2 mm. Each of the first and second lens sheet 42 and 44 has a plurality of triangle prisms extending horizontally or vertically and arranged on the rear surface thereof. The first and second lens sheets 42 and 44 have a function for correcting the direction of the light passed from the optical guide plate 38 to form a substantially parallel ray on the front screen of the LCD panel 12.
The light source 36 of the backlight unit 14 is implemented by a cylindrical elongate lamp extending along the light receiving edge 38b of the optical conductive plate 38. A metallic reflecting member 54 having a xe2x80x9c]xe2x80x9d shape in cross section is disposed for encircling the lamp 36. The metallic reflecting member 54 has a first edge abutted with the light receiving edge 38b near the front side thereof, and a second edge sandwiched between the holder 18 and the reflective sheet 50 disposed at the rear surface of the optical conductive plate 38.
The backlight chassis 56, as mentioned before, is made of an opaque plastic material and is disposed for positioning and supporting the optical conductive plate 38, the optical sheet assembly 48, the lamp 36 and the metallic reflecting member 54 with respect to the LCD panel 12 while encircling these members. A spacer 58 made of a plastic material is disposed between the backlight chassis 56 and the metallic reflecting member 54.
FIG. 3 shows, in a sectional view, a side edge portion 60 of a conventional LCD device 10A having configurations such as shown in FIGS. 1 and 2, wherein FIG. 3 is taken along a line corresponding to line IIIxe2x80x94III in FIG. 1. In FIG. 3, the optical conductive plate 38 has an edge 38c, other than the light receiving edge 38b, the edge 38c being flush with the edges of the first scattering sheet 40, the first lens sheet 42 and the second lens sheet 44 of the optical sheet assembly 48. The edge 38c opposes the inner surface 56a of the backlight chassis 56. The second scattering sheet 46 of the optical sheet assembly 48 has an extended edge 46a protruding from the edges of the first scattering sheet 40 etc. of the optical sheet assembly 48, and mounted on a step 56b of the backlight chassis 56, with an intervention of a cushion member 57 disposed therebetween.
The LC drivers 32 and 34 are mounted on a support member 62 disposed at the rear side of the reflective sheet 50. TCPs (tape carrier packages) 66 extend from the LC drivers 32 and 34 toward the front side of the LCD panel 12 for transferring driving signals for the LCD panel 12.
FIG. 4 is a schematic view showing the situation wherein the screen of the conventional LCD device 10A is observed by a human eye with an angle xe2x80x9caxe2x80x9d which is the supplementary angle of the viewing angle of the LCD panel. In the vicinity of the black matrix 30, the human eye observes a bright line, which passes the space between the edge 38c of the optical conductive plate 38 and the inner surface 56a of the backlight chassis 56 while being repetitively reflected by the edge 38c of the optical conductive plate 38 and the inner surface 56a of the backlight chassis 56.
The bright line appearing in the vicinity of the image of the black matrix 30 of the LCD device significantly degrades the image quality of the LCD device, and is thus undesirable.
In view of the above, it is an object of the present invention to provide an LCD device having an excellent image quality by suppressing the bright line as encountered in the conventional LCD device.
The present invention provides, in a preferred embodiment thereof, a liquid crystal display (LCD) device including: an LCD panel; a backlight unit including a light source, an optical conductive plate including a light receiving edge for receiving therein light from the light source, three remaining edges, and a light emitting surface for irradiating therethrough the light received through the light receiving edge toward the LCD panel, and an optical sheet assembly including a first light scattering sheet, a first lens sheet, a second lens sheet and a second light scattering sheet consecutively formed on the light emitting surface; and a backlight chassis for positioning the light source, the optical conductive plate and the optical sheet assembly with respect to the LCD panel, wherein at least the first and second lens sheets among the optical sheet assembly have extended edges adjacent to one of the three remaining edges, the extended edges protruding from the one of the three remaining edges toward the backlight chassis.
In accordance with the LCD device of the present invention, the bright line which degraded the image quality of the conventional LCD device is suppressed by the extended edge of the lens sheet.